| 其他摘要 | The core component of the reflecting astronomical telescope is the reflecting primary mirror, and as the aperture of the reflecting astronomical telescope gradually increases, the primary mirror does not flip and is coated from top to bottom has become an inevitable choice. Astronomical telescopes have high requirements for the imaging quality of optical systems, and the uneven distribution of the thickness of the reflective film will increase the surface shape error of the primary mirror and affect the imaging quality of the telescope. Film thickness uniformity refers to the change of film thickness with the change of substrate surface position, which is an important indicator for the preparation of high-performance optical films. In this paper, the study on controlling the thickness uniformity of large-aperture mirror film during top-down and multi-evaporation source coating is carried out, which provides a reference for the coating of 2.4m telescope primary mirror and the non-flipping coating of larger size primary mirror, which has practical application value.Based on the cosine distribution law followed by vacuum thermal evaporation, combined with the geometry of ZZ3200 vacuum coater and the actual needs of 2.4m telescope coating, the film thickness calculation program is written, the theoretical distribution of film thickness is simulated, and the optimal design method of the uniformity of two film thicknesses is given. Method 1: Considering the circular hole structure in the middle of the 2.4m main mirror, the double circle evaporation source is arranged, and the results show that the distance from the inner and outer ring evaporation source to the mirror rotation center is 10cm and 130cm, respectively, and when the number of outer ring evaporation sources is close to 12 times that of the inner ring, the PV value of film thickness uniformity is 1.85%, which is very suitable for large-diameter mirror coating with a circular hole structure in the center. Method 2: Combined with the vacuum chamber structure of the coater, the correction mask is added at a suitable position inside the evaporation source, the results show that the shielding height of the mask is 5.2cm, the radius of curvature is 123cm, when the installation error of the mask does not exceed 3mm, the PV value of film thickness uniformity is less than 4%, which has good universality for top-down large-diameter mirror coating.According to the simulation analysis of the optimization scheme of the correction mask, combined with the actual situation of ZZ3200 vacuum coating machine, the coating experiment was carried out by processing and debugging the correction mask. The results show that the PV value of film thickness uniformity obtained by the actual coating experiment is 6.10%, and the RMS is 1.61%, and the change trend of the measured film thickness distribution is basically consistent with the optimization results of the corrected mask, and the corrected mask has a good control effect on the unevenness of film thickness, which can reduce the influence of the unevenness of the thickness of the reflective film on the error of the primary mirror type. The feasibility and practicality of the optimization method for correcting the uniformity of the thickness of the mask film proposed in this paper have been verified experimentally, which can not only be used to guide the development of large-size coating machines, but also provide reference for the coating of large-diameter astronomical mirrors. |
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